1. Technical Field
Exemplary aspects of the present disclosure generally relate to an image forming apparatus and a gear transmission device, and more particularly to an image forming apparatus including the gear transmission device equipped with an internal gear as a first-stage driven gear driven by a motor.
2. Description of the Related Art
Generally, known gear drive assemblies that drive a target at a low speed and a high torque include an external gear and a first-stage driven gear that meshes with the external gear. The external gear is a gear with teeth formed on the outer surface of a cylinder or a cone, and is attached to a rotary shaft of a drive motor serving as a drive source. The first-stage driven gear meshing with the external gear is configured to transmit power at a high speed and low torque. In other words, the external gear of the motor is designed to have a small number of teeth (pitch circle diameter) for acceleration. By contrast, the pitch circle diameter of the first-stage gear is relatively wide to achieve a greater deceleration ratio.
However, if the number of gear teeth of the external gear of the drive motor is reduced, an adequate contact ratio between the first-stage driven gear and the external gear cannot be secured, thereby causing fluctuation of rotation, noise, and vibration. In order to reduce noise and vibration, in one approach, grease is injected between gear teeth meshing with each other. However, the noise and vibration still remain. Furthermore, injecting grease for multiple times causes a higher risk of a foreign substance getting into the mesh portion between the gear teeth, which results in noise, degradation of rotation accuracy, and damage to the gear.
In view of the above, in order to reduce the noise and vibration, JP-H11-311302-A proposes using an internal gear as the first-stage gear meshing with the external gear attached to the rotary shaft of the drive motor.
In this configuration, an opposite side of the meshing side of the external gear is exposed to an internal space of the internal gear so that a sound of gears meshing with each other resonates in the internal space of the internal gear and leaks outside. Furthermore, if the durability of the internal gear is not sufficient, the vibration caused by the gear mesh resonates with the internal gear, causing the vibration to spread outside.
In view of the above, there is an unsolved need for a gear transmission device that reliably prevents undesirable noise and vibration from dispersing from a driven gear.